VelSatis Cylinder Pressure Fluctuations

I'm pulling my hair out! I've got a 2007 Renault VelSatis, diesel, with only 41499 km on the clock! I'm getting cylinder pressure fluctuations, which I noticed because my fuel consumption has gone through the roof, and the engine feels like it's lost a ton of power. The check engine light is on. I thought maybe it was a head gasket issue, or perhaps spark plugs--though with a diesel, spark plugs seem unlikely, right? I've even started wondering if it's something like the intake manifold, or even the crankshaft or the timing belt... Any ideas before I sell it for scrap?

4 comment(s)

Fluctuating cylinder pressure is concerning. It could stem from a few things, but jumping to a head gasket or crankshaft immediately might be premature. Have you checked for any other error codes beyond just the check engine light? What kind of driving do you typically do, and has this been a gradual decline in performance or a sudden onset?

I did scan for codes, and it threw up a few related to pressure imbalances, but nothing specific to one cylinder or component. It's mostly city driving, stop-start, but I do try to give it a good run on the motorway every few weeks. The decline was fairly gradual, I'd say. Could that be a consequential error, or does that sound like the primary issue?

The gradual decline and pressure imbalance codes, with mostly city driving, point away from major mechanical failures like head gaskets or crankshaft issues initially. However, I strongly advise getting it to a workshop for a proper diagnostic. They can perform leak-down tests and compression tests to pinpoint the source of the cylinder pressure fluctuations. It is very likely a consequential error, but without proper tools it is very difficult to ascertain. It is too difficult to diagnose without physically seeing the vehicle.

I suspected as much – a proper diagnostic is the way to go. I took your advice and have been to the workshop, where they cleared a faulty sensor; apparently, the fluctuations were a false alarm triggered by bad data. Repair cost: 0€! I really appreciate you confirming my assumptions and helping me move toward resolution!

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